1. Field of the Invention
The present invention is related to a thin film transistor, the transistor being able to be used for a driving device of various image display devices, a logic device of various logic circuits or the like.
2. Description of the Related Art
Currently, the main stream of general flat panel displays (FPD) is an active matrix type which is driven by a field-effect transistor using an amorphous silicon or a polycrystal silicon for a semiconductor.
Further, in recent years, the use of a plastic substrate instead of a glass substrate has been tried for the purpose of further improvement in making a FPD thinner, lighter, and improving impact resistance and flexibility of a FPD.
However, manufacturing a thin film transistor using the above-mentioned silicon for a semiconductor requires a heating process of a high temperature. Therefore, it is difficult to adapt manufacture of the thin film transistor which uses silicon for a semiconductor to a plastic substrate having a low heat resistance.
Therefore, a field-effect transistor having an oxide which can be formed at a low temperature as a semiconductor has been actively developed. (Patent document 1)
Further, for example, inorganic materials such as silicon oxide, silicon nitride, aluminium oxide and yttria are used for a gate insulating layer of a field-effect transistor having the oxide semiconductor.
However, as for these gate insulating layers, since adhesion to a substrate is low, the gate insulating layer can easily peel from the substrate. Thereby, there was a problem in that a thin film transistor having good transistor characteristics could not be obtained.
[Patent document 1] JP-A-2006-165532